I. Field of the Invention
The present invention concerns HR polyurethane foams. More particularly, the present invention concerns urethane formation promoting active-hydrogen-containing compositions for use in the preparation of HR polyurethane foams. Even more particularly, the present invention concerns stabilized, reactive active-hydrogen-containing compositions for use in HR polyurethane foams.
II. Prior Art
The preparation of HR or high resiliency polyurethane foams with high load bearing and strength properties by the reaction of a polyol or other active-hydrogen-containing compound and an organic polyisocyanate in the presence of a cross-linking agent is well known. Until recently, the most widely used cross-linking agent was 4,4'-methylene-bis-(2-chloroaniline) (MOCA). This compound, which is sterically hindered and negative-substituted, evidences a reactivity rate substantially equal to that of the active hydrogen compound with the isocyanate. Thus, it permitted urethane formation at a good rate, in deference to polyurea formation. However MOCA is a suspected carcinogen and has, thus, been virtually banned. Therefore, the art now seeks viable alternatives to MOCA.
Diamine cross-linking agents which have now been investigated include methylene dianiline, isophorone diamine, and bis-(p-aminocyclohexyl)methane. However, these diamines are highly reactive with isocyanate. Thus, when employed as cross-linking agents with active-hydrogen-containing compounds, they tend to form insoluble polyureas with the isocyanate before urethane formation occurs. Hence, it is readily appreciated that polyurethane foam formation in the presence of highly reactive diamine cross-linking agents can be extremely difficult. In copending U.S. patent application Ser. No. 842,621, filed Oct. 17, 1977 now U.S. Pat. No. 4,176,218 for "HIGH RESILIENCE FLEXIBLE FOAMED POLYURETHANES, FOAMABLE MIXTURES AND PROCESS THEREFOR", the disclosure of which is hereby incorporated by reference, the use of highly reactive cross-linking diamines is disclosed. It has been experienced that polyurethane foam systems incorporating these discoveries are extremely sensitive to external conditions, such as variation in foam formulation, moisture content and the like. Such sensitivity inhibits consistency in foaming. However, because of such difficulty in preparing foams due to the diamine reactivity, the benefits of the diamines cannot be fully achieved.
Therefore, it is to be appreciated that the use of highly reactive diamines would be greatly enhanced if their reactivity could be lessened to equal or approximate that of urethane formation promoting active-hydrogen-containing compound, thereby enabling the preparation of HR polyurethane foams therefrom.